This invention relates to a novel assembly and method suitable for writing high density data on a ferroelectric media, the novel assembly being readily further equipped so that it can have a reading capability.
The present invention builds upon the notion of a ferroelectric media. The basic physics of a ferroelectric media are now briefly stated, in order to facilitate an understanding of the present invention and its purview.
In order to give an overview, the term ferroelectricity is conventionally used for certain crystalline dielectric materials that show a permanent polarization. (This is analogous in many ways to the permanent magnetization exhibited by ferromagnetic materials.) For these crystalline dielectric materials, accordingly, a charge displacement may be induced under the influence of an applied electric field. The polarization associated with this displacement creates an internal field, which both increases and stabilizes the induced polarization, with the result that a portion of this polarization remains even after the external field is turned off.
More specifically, an electric field Ei inside a dielectric material induces an electric dipole moment p. The potential energy of this electric dipole moment is given by xe2x88x92pEi. The average value ({overscore (pxc2x7cos(xcex8))}). of this electric dipole moment in the direction of the applied field can be calculated using a Boltzmann distribution (exp(xe2x88x92pxc2x7Ei cos(xcex8)/kT)). For a substance with n elementary dipoles per unit volume, the electric polarization (dipole moment per unit area) is then given by P=n ({overscore (pxc2x7cos(xcex8))}). Now it needs to be considered that the field Ei acting upon a dipole in the material is the sum of applied E, and that arising from the neighboring dipoles (xcexP). Therefore, the dipole aligning force depends partially upon the degree of alignment (electric polarization) already prevailing; any increase in the electric polarization will result in an increase in the aligning force, which, in turn, will result in an increase in the electric polarization, etc. In short, a cumulative effect is expected. In this way, electric polarization, once triggered, can occur without the application of an external field.
More phenomenologically, and in analogy to B-H hysteresis loops, the polarization of a ferroelectric media increases non-linearly with the field. The susceptibility depends on the applied field. As the field polarizes a typical ferroelectric media, the susceptibilities are very high ( greater than 500). However, as the field increases, the polarization saturates. Once the media is polarized and the field is turned off, it exhibits a remaining polarization, also known as remanence. The polarizing field must be negative, to a value known as coercive force, in order to remove this remaining polarization. We note that the value of the coercive force depends on the temperature. Typically, as the temperature increases, the coercive field decreases rapidly until it reaches the Curie-temperature Tc. Above the Curie temperature, the thermal fluctuations are too large, so that the material loses its electric polarization.
present invention discloses a novel assembly for writing high density data on a ferroelectric media. To this end, the novel assembly employs a thermal heater which can lower the ferroelectric coercivity of the ferroelectric media by heating the material close or above the Curie-temperature, preferably on a local scale, e.g., preferably by way of a substantially near-field coupling. Preferably, an external electric bias field can then polarize the ferroelectric material. Writing or recording on the ferroelectric media can be enabled by using an information signal for modulating the electric bias field or using an information signal for modulating the power of the incident thermal wave to the ferroelectric media. The remaining polarization on the ferroelectric media can be read by suitable employment of an electric field sensor.
Accordingly, in a first aspect of the present invention, we disclose an assembly for writing high-density data on a recording media as a series of tags comprising a ferroelectric information bit pattern, the assembly comprising:
1) an electric bias field generator for applying an electric bias field on the media;
2) a thermal heater for generating and directing an incident thermal wave to the media; and
3) a controller for coordinating a mutual positioning of the incident thermal wave and the ferroelectric media for inducing a direct thermal coupling therebetween; the assembly acting as a writer by operating the controller so that writing is enabled by using an information signal for modulating a localized thermal wave generated in the vicinity of the ferroelectric media.
In a second aspect of the present invention, we disclose a method for writing high-density data on a recording media as a series of tags comprising a ferroelectric information bit pattern, the method comprising the steps of:
1) applying an electric bias field on the media;
2) generating and directing an incident thermal wave to the media;
3) coordinating a mutual positioning of the incident thermal wave and the ferroelectric media for inducing a direct thermal coupling therebetween; and
4) operating the controller so that writing is enabled by using an information signal for modulating a localized thermal wave generated in the vicinity of the ferroelectric media.